A Synergistic Three-Phase, Triple-Conducting Air Electrode for Reversible Proton-Conducting Solid Oxide Cells

Reversible proton-conducting solid oxide cells (R-PSOCs) have the potential to be the most efficient and cost-effective electrochemical device for energy storage and conversion. A breakthrough in air electrode material development is vital to minimizing the energy loss and degradation of R-PSOCs. Here we report a class of triple-conducting air electrode materials by judiciously doping transition- and rare-earth metal ions into a proton-conducting electrolyte material, which demonstrate outstanding activity and durability for R-PSOC applications. The optimized composition Ba_0.9Pr_0.1Hf_0.1Y_0.1Co_0.8O_3-δ (BPHYC) consists of three phases, which have a synergistic effect on enhancing the performance, as revealed from electrochemical analysis and theoretical calculations. When applied to R-PSOCs operated at 600 °C, a peak power density of 1.37 W cm^-2 is demonstrated in the fuel cell mode, and a current density of 2.40 A cm^-2 is achieved at a cell voltage of 1.3 V in the water electrolysis mode under stable operation for hundreds of hours.